The optical quality of a spectacle lens, either single vision or progressive, can be improved for the wearer by using freeform surfaces, i.e., surfaces which may freely be formed during the manufacturing process of the spectacle lens and which do not need to show axial symmetry or rotational symmetry. The spectacle lens can be optimized with respect to individual prescription data of the wearer, as well as to individual as-worn position and frame data. Such an optimization requires a target design. The target design typically includes a target distribution of optical aberrations for the wearer, e.g., astigmatic error, power error, prism, possibly higher order errors like coma seen in the beam path running through a spectacle lens, through the pupil and through the eye's center of rotation, and also may include surface properties of the freeform surface, such as surface astigmatism, and includes an assigned power distribution.
Specific target designs are generally connected with a specific lens product. Each lens product may have a number of associated target distributions to accommodate the range of prescription power, addition power, refractive index, and progression length. Currently, the main option that eye care professionals (ECPs) have for satisfying the specific needs of the customer is to rely on product claims and experience; they do not have access to either the target distributions, or the details of the final performance of the produced lens.
It would be desirable for the ECPs to have more control over the optical performance of the spectacle lenses which they provide to their patients. Even products that can be varied, e.g., in progression length/frame size or use/lifestyle profiles, may only roughly fulfill the desired requirements of the spectacle lens. These requirements can be fairly general, such as specifying the relative importance of the various zones; e.g., distance vision zone, intermediate vision zone (progression zone) and near vision zone. However, the requirements can also be more detailed, and include a desired optical power distribution and/or distribution of aberrations for the wearer and/or surface properties of the spectacle lens. In general, it will not be possible to achieve all of the desired, possibly contradictory, properties of the lens, and specifying contradictory properties can result in a lens having optical properties significantly different than intended.
There are several approaches to give the ECP more control over the optical performance of the spectacle lenses which they provide to their patients. For example, U.S. Pat. No. 7,344,245 B2 discloses a method of designing a progressive lens in which the shape of a reference lens is modified by a morphing process based on the wearer's preferred value for one or more design features. U.S. Pat. No. 8,128,226 B2 describes a method for the determination of a progressive lens personalized for a specific frame chosen by a given wearer. In this method, a personalized distribution of the power and the astigmatic error is calculated starting from an initial distribution of the power and the astigmatic error by using a transformation, which is based on the frame chosen by the wearer.
U.S. Pat. No. 8,434,025 B2 discloses a method of designing and/or selecting a progressive addition lens design for a wearer. In an embodiment, the method includes displaying a graphical representation of an initial progressive addition lens design including design parameters having design values. A user interface is provided including, for each of one or more of the design parameters, a control that is adjustable over a range of levels, each level in the range being associated with a corresponding value of the respective design parameter. A control is adjusted to select a level and the selection is processed so as to substantially simultaneously update the displayed graphical representation in accordance with the selected level to provide a modified progressive lens design. A system for designing and/or selecting a progressive addition lens design for a wearer is also disclosed in U.S. Pat. No. 8,434,025 B2. However, the method and the system of U.S. Pat. No. 8,434,025 B2 only allow for adjusting a selection of design parameters over a predetermined range given by the adjustable controls.
Considering the teaching of U.S. Pat. No. 8,434,025 B2 the present disclosure provides a method and device for establishing a target design which method is useful for an ECP in finding a compromise in achieving as many of the desired, possibly contradictory, properties of a spectacle lens as possible. In particular, the proposed method and the proposed device increase the freedom of the ECP in specifying a desired target design as compared to U.S. Pat. No. 8,434,025 B2.